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If all goes as planned, Commander Scott Kelly will be back on Earth Tuesday, but his mission is far from over. After he lands in Kazakhstan, researchers are going to be swarming Kelly like biology students with their first lab rat.

A key goal of Kelly’s mission has been to identify the physiological and biochemical effects of prolonged space flight so NASA can figure out what crews might experience en route to Mars, which would be a 30-month mission. During his American-record-setting 340 consecutive days in orbit, Kelly has collected his blood and urine for scientists to analyze, and conducted experiments on his physiology, cognition, and more. But NASA isn’t done with him. Once he’s back, researchers will keep studying him to see whether a year in space has made him farsighted or stupid, among other things.

Here are some of the health effects that scientists will be monitoring Kelly for:


1. Where’d I leave my &*$#! glasses?

In microgravity, blood and other fluids float toward the head. That can cause pressure on the back of the eye and harm vision. One astronaut reportedly couldn’t read the reentry checklist, and more than 30 percent of US astronauts have experienced changes in their eyes after months-long stays on the space station. So many become farsighted, in fact, that the space station keeps a supply of eyeglasses.

During his mission Kelly has measured how fluid distribution in his body has changed (using ultrasound and other noninvasive techniques); once he’s back, scientists plan to look for “tortuosity and kinking” in Kelly’s optic nerve, according to Japanese astronaut Dr. Chiaki Mukai, who is leading a vision study for NASA. She’ll measure him again 10, 30, and 180 days after he lands to see if any changes reverse. 


2. Feeling forgetful

Astronauts’ redistribution of bodily fluids can also increase cranial pressure enough to affect the brain, scientists suspect; some returning astronauts have had trouble walking a straight line and turning corners cleanly. NASA’s Jacob Bloomberg will test for such “postflight changes in functional performance,” including sensory and motor skills and muscle physiology, by testing Kelly up to 30 days after he lands.

Kelly has also been undergoing testing for fine motor control, memory, perception, reaction speed, and other brain functions as part of a study by Dr. Mathias Basner of the University of Pennsylvania to quantify the mental fuzziness or “space fog” that many astronauts complain about. He’ll continue those tests for three months after he lands. Can he click on smaller and smaller squares on a computer screen? Remember 10 three-dimensional shapes (for instance, a rectangle floating in one corner of a transparent box) for several minutes? Recall which fractal, in a sequence popping up on a computer screen, appeared two before the current one?

3. Weak muscles

Kelly told Air & Space magazine that postmission “you feel bad for a month, and I’ve never felt completely normal” after his earlier space sojourns. The woes include bone loss and muscle wasting (both the result of less gravity pulling on those tissues), headaches (that fluid redistribution thing again), and poor sleep (a space station average of 6.1 hours per 24). The station’s old exercise equipment didn’t provide enough resistance to prevent muscle atrophy, deterioration of heart function, and bone loss, but a new treadmill and resistance machine have allowed astronauts to run faster and do resistance exercises at heavier loads. Scientists will evaluate if that reduced Kelly’s loss of muscle, bone, and cardiovascular functions. He’s got at least another month of tests once he’s back on Earth.

4. Genetic changes

Scott Kelly’s twin, Mark, is a retired astronaut, so scientists will compare the brothers to see how Scott’s DNA, proteins, gut microbes, immune system, and cognitive performance changed relative to Mark’s. Kelly has been a virtual pincushion during his flight, with blood draws (and urine and saliva samples) that will be analyzed for clues to his levels of stress hormones, his immune system function, even the length of his telomeres (sections of chromosomes that have something to do with aging). Many of those measurements, which will continue for years in some cases, will be compared to Mark’s so scientists can subtract out normal aging changes from what 340 days in space does to a body.

5. Altered circulation

Experimental testing to evaluate whether a year in space affected the structure and function of Kelly’s arteries will have him undergoing ultrasounds through 2021.

6. Microbe makeup

Kelly and other space stationeers have been swabbing their noses, mouths, and skin, and collecting fecal samples, to see how their collection of bacteria, viruses, and other (mostly harmless) microbes changed in microgravity. That’s important because the booming field of microbiome research suggests that the kind and quantity of bugs in the microbiome affect metabolism, immune function, and other systems that need to be firing on all cylinders during a Mars mission.

Biologist Hernan Lorenzi of the J. Craig Venter Institute, who leads the microbiome study, has already discovered that some gut bacteria become more abundant and some less, while nose microbes decrease (probably because of the clean filtered air aboard the station). Kelly can look forward to six months of additional sampling.